Threaded joint for pipes

Abstract

A threaded joint for pipes comprises a pin and a box, each having a threaded and unthreaded portion metal contact surface. The unthreaded metal contact portion includes a sealing surface and a shoulder surface, the shoulder surface of the pin located on the pin end surface. A non-contacting region where the pin and the box do not contact each other exists between the sealing surfaces and the shoulder surfaces of the pin and the box. One or more grooves is formed in at least one of the pin and the box shoulder surfaces and extending to the non-contacting region and to the interior of the joint. At least one of the contact surfaces has a solid lubricating coating exhibiting plastic or viscoplastic rheological behavior. A total volume V (mm3) of the grooves and coating weight W (g) of the solid lubricating coating satisfy the equation V / W≧24 (mm3 / g).

Description

TECHNICAL FIELD[0001]This invention relates to a threaded joint for pipes (also called a tubular threaded joint) suitable for connecting oil country tubular goods and having grooves on its shoulder surface in order to allow a high pressure fluid to escape. Specifically, it relates to a threaded joint for pipes which prevents a deterioration in to the performance of the grooves by a solid lubricant coating.BACKGROUND ART[0002]In recent years, oil wells are being deeper and are being developed in increasingly severe environments. For this reason, there is a strong desire that tubular threaded joints which are used to connect oil country tubular goods including tubing and casing for oil or gas wells have increased resistance to compression under internal and external pressures and improved sealing properties.[0003]FIG. 1A is a cross-sectional view schematically showing the structure of a typical threaded joint for pipes, FIG. 1B is an enlarged schematic cross-sectional view of portion ...

AI Technical Summary

Benefits of technology

This invention relates to a threaded joint for pipes that has a solid lubricating coating for better performance. The coating prevents clogging of grooves in the joint, which can compromise its gas tightness. The entire surface of the pin and box is coated for better adhesion. However, a non-contacting region between the sealing surface and shoulder surface can still get filled with the coating, which can malfunction as a leak path. This invention improves galling resistance and rust prevention with the added benefit of the solid lubricating coating.

Problems solved by technology

If this occurs, due to the fact that the fluidity of the solid lubricating coating is much lower than that of liquid lubricating grease, the grooves are clogged and cannot function as a leak path.

As a result, the pressure in the non-contacting region 13 is increased, resulting in a deterioration of the gas tightness of the threaded joint which is achieved by the sealing surfaces.

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